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Understanding the basic anatomy and physiology of the human body

The respiratory system

The respiratory system is composed of various structures and organs that ensure that the body is able to maintain its internal environment through the exchange of air between the lungs and the atmosphere. In order to survive the body needs a constant supply of oxygen, which it obtains from the air.

The body also needs to dispose of carbon dioxide, made as a waste product from the process of cell metabolism. The ingestion of oxygen and the discarding of carbon dioxide, occurs through the process of respiration or breathing.

Click here to roll over a diagram to locate the major structures and functions of the respiratory system.


The respiratory system is comprised of the:

The respiratory system contains the upper and the lower respiratory tracts. The upper respiratory tract contains the respiratory organs located outside the chest cavity: the nose and the nasal cavities, pharynx, larynx and upper trachea.

The lower respiratory tract consists of organs located in the chest cavity: the lower trachea, bronchi, bronchioles, alveoli and the lungs.

The lower parts of the bronchi, the bronchioles and alveoli, are all located in the lungs. The alveoli are the point at which gas exchange takes place.

The pleura are a membrane that covers the lungs.

The muscles that form the chest cavity are also part of the lower respiratory tract. The respiratory centre in the brain, which is located in the medulla oblongata, regulates breathing. (Herlihy et al. 2000).


The function of the respiratory system is to supply oxygen and to remove carbon dioxide from cells. Oxygen is needed by cells to produce heat and energy. In using oxygen, the cells produce carbon dioxide as waste.

Inhaled air is moistened and warmed as it passes through the upper respiratory tract - the nose, the pharynx and the larynx. The clean air passes on through the lower respiratory tract - the trachea and lungs where the exchange of gases takes place (Sorrentino, 1997).


Respiration involves the passage of air in and out of the lungs.

Air passes from nose to the pharynx to the larynx to the trachea to the left and right bronchus to the bronchioles to the alveoli (where a gas exchange takes place and oxygen and carbon dioxide are exchanged in the pulmonary capillaries) (Herlihy et al. 2000).

Click here to see a diagram which will help you understand how gases are exchanged within the respiratory system.

Air enters the body via the nasal passages, where it is warmed, moistened and filtered. Air then passes down through the pharynx and into the larynx and trachea. The air continues into the right and left bronchi and then into the lungs. In the lungs the bronchi then branch into smaller bronchioles, that each have air sacs called alveoli, attached to them. The exchange of oxygen and carbon dioxide takes place at this level, between the alveoli and the blood capillaries. Through this process oxygen enters the bloodstream and can be transported around the body.

Activity 7

In these activities you will check your understanding of the respiratory system.

  1. Click here
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